What are Ordovician fish?

The term "Ordovician fish" is a bit misleading. While the Ordovician period (485.4 to 443.8 million years ago) was a crucial time for the evolution of early vertebrates, true fish as we know them today did not exist during this time.

Here's a breakdown of what existed during the Ordovician:

* Early Vertebrates: The Ordovician saw the emergence of jawless, armored fish known as ostracoderms. These were primitive fish-like creatures with bony plates covering their bodies.

* Conodonts: These enigmatic creatures are often considered to be the earliest vertebrates. Their fossils are primarily tooth-like structures, making their exact appearance and lifestyle a mystery.

* Absence of Jawed Fish: Jawed fish (gnathostomes), which represent the vast majority of modern fish, did not evolve until the Silurian period, following the Ordovician.

So, the Ordovician "fish" were actually more like early ancestors of fish, not the modern fish we're familiar with. They were quite different in appearance and lacked jaws, a key evolutionary development that would later lead to the diversification of fish.

In summary, the Ordovician period is notable for the emergence of the earliest vertebrates, but true fish, as we know them, evolved later.